Errors can occur during the transmission of data from a transmitter/receiver station, for example, a base station of a mobile telephone system, to a transmitter/receiver device, for example, a mobile telephone, and during the decoding implemented in that context. In determining error rates for that context, a data transmission is generally carried out between a measuring device and the mobile telephone, wherein the base station of the mobile telephone system is emulated by the measuring device. In this context, the measuring device is structured in such a manner that, like the base station itself, it fulfills all requirements of the relevant standard, that is to say, it also supports measures for software-assisted error correction.
With more recent mobile-telephone systems, for example, in the standard for EGPRS (Enhance General Packet Radio Service), an incremental increase in redundancy is implemented in order to increase security during transmission of data. This means that after the transmission of a first data block coded according to a given convolutional coding scheme, tests are carried out at the receiver end to determine whether the transmission and the decoding of the received data has taken place without error. If the data record received in this manner contains errors, the transmission of further, redundant data from the base station is requested by the receiver.
This so-called “Incremental Redundancy” is described, for example, in U.S. Pat. No. 5,657,325.
In this context, the redundant data are generated together with the first data block from an originally entered data record by convolutional coding, wherein redundant information is generated for each item of information in the original data record. For example, with the coder MCS9 in the context of the EGPRS standard, three bits are generated from every bit. To avoid the necessity to transmit this threefold data volume in every case, bits are removed from this threefold data volume according to a punctuation scheme and stored in a memory. The remaining bits are transmitted as a first data block to the receiver, where they are evaluated.
In the event of an error transmission and evaluation of the first data block received, the receiver reports the error reception of the data to the transmitter, whereupon redundant data in a second data block, formed according to a second punctuation scheme by the elimination of bits from the threefold data volume, are transmitted to the receiver. Using these redundant data, the errors, which have occurred in the reception of the first data block can be corrected or another redundant data block is again requested.
In the context of a production testing system, for example, for evaluating the quality of a mobile telephone, the procedure described provides the disadvantage that when determining an error rate, which is caused by the mobile telephone, the errors originally occurring during the transmission are eliminated as a result of the incremental redundancy, and an evaluation of the actual errors caused by the hardware of the mobile telephone without correction by the software using the redundant data is therefore not possible.